This invention relates to a precombustion chamber construction of an internal combustion engine and more particularly to a precombustion chamber made of a ceramic material to improve thermal efficiency of an engine and durability and heat-resistance of the precombustion chamber and having a metal ring fitted on ceramic members forming the precombustion chamber to facilitate handling the precombustion chamber.
In order to improve thermal efficiency of engines, characteristics of exhaust gases and durability of precombustion chambers of internal combustion engines, particularly diesel engines, various attempts have been made to form part or all of turbulence chambers of internal combustion engines by ceramic materials utilizing their superior charcteristics such as heat-resistance and thermal insulating capability.
However, as the ceramic materials have thermal expansion coefficients smaller than those of materials for constituting cylinder heads, for example, cast irons or aluminum alloys, supporting forces of the cylinder heads for the precombustion chambers tend to decrease when the cylinder heads are at high temperatures. With a precombustion chamber construction of a ceramic material consisting of upper and lower members, particularly, there is a tendency of the members to be rotatively moved relative to each other, so that an injection hole for communicating a main chamber and the precombustion chamber becomes out of its proper position to disturb normal ignition and explosion of a fuel. Moreover, when the upper and lower members are rotated relative to each other to an extreme extent, a fuel injection nozzle and a glow-plug may be often damaged by the movement.
In Japanese Laid-open Utility Model Application NO. 58-191,330 to avoid this, as shown in FIG. 1, a precombustion chamber construction of an internal combustion engine consists of a lower chamber 3a and an upper chamber 3b made of a ceramic material and having pin receiving apertures 7 and 15 formed in the respective lower and upper chambers. Moreover, a cylinder head 1 is formed with a pin engaging recess 16 straight extending along an inner surface of a cavity of the cylinder head from its lower surface to the ceramic upper chamber 3b. With this precombustion chamber construction, the pins 9 are inserted in the pin receiving apertures 7 and 15, so that depression engaging portions 9b of the pins 9 engage within the pin engaging recess 16 so as to be press-fitted therein with an interference, thereby fixing the ceramic chamber 3 to the metal cylinder head 1.
With this arrangement, however, clearances occur between the ceramic members and the metal members during the operation of the engine due to large differences in thermal expansion coefficient between the ceramic material and the metals, so that parts of explosion energy caused by ignition and explosion of a fuel injected into air which has been at high temperature and high pressure by rapid compression would escape into the pin engaging recess to lower the output of the engine.
In assembling the precombustion chamber construction, moreover, the upper and lower chambers made of the ceramic material having the pins extending from the chambers, respectively, must be inserted separately into the precombustion receiving cavity formed in a lower side of the cylinder head. Accordingly, the assembling operation of the precombustion chamber construction is very troublesome because it is required to take care not to damage the ceramic members which are of high strength but brittle.